1. Field of the Invention
The present invention relates to a magnetic recording medium provided with a servo-area on which information used for positioning a magnetic head at a target position is recorded, and a magnetic recording/reproducing apparatus that carries out a reproducing process on such a magnetic recording medium.
2. Description of the Related Art
In a hard disk drive (HDD), a controlling process in which, upon positioning a magnetic head at a specified track, after the magnetic head has been allowed to seek for the specified track, a relative distance of the magnetic head from the center position of the track is found to position the magnetic head on the track, needs to be carried out.
In order to carry out such a positioning control, servo data of a magnetic section recorded on a burst area in the servo-area of the magnetic recording medium is reproduced so that the positioning control of the magnetic head is carried out. The burst area is divided into bursts A, B, C and D made of magnetic sections recorded by four types of burst recording patterns having different positioning phases in the radius direction of the magnetic recording medium, and based upon an amplitude value of a reproduced signal generated when the magnetic head crosses each of the bursts A, B, C and D, positional deviation information indicating the relative distance of the magnetic head from the center position of the track is found so that the magnetic head is positioned at the track center position; thus, the positioning control is carried out.
In recent years, with respect to the magnetic recording medium, so-called patterned media in which servo-data to be recorded in a servo-area is embedded and formed as a magnetic section upon manufacturing the magnetic recording medium have received much attention.
In these pattern media, it is difficult to ensure the shape stability of the magnetic sections of the respective bursts A, B, C and D over the entire surface, and noise to a reproduced signal from the magnetic sections tends to increase to cause a difficulty in obtaining accurate position deviation information, causing the problem that there is a failure in positioning control for the magnetic head.
Moreover, upon manufacturing patterned media, in an attempt to stably carry out transferring and forming processes over the entire surface, it is preferable to reduce fluctuations in the ratio of irregularities of the magnetic section in the servo-area to a level as small as possible; however, within the servo-area, the ratio of irregularities becomes 50% in a preamble area and an address area while the ratio thereof becomes 25% in a burst area, with the result that it becomes difficult to manufacture a disk by carrying out transferring and forming processes over the entire surface.
In order to solve this problem, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-169032 and JP-A No. 6-68623 have disclosed a technique, which, upon processing a reproduced signal of the servo-data, detects a phase difference of the reproduced signal of the servo-data. JP-A No. 6-231552, which relates to a process used for detecting position deviation information corresponding to a relative distance of the magnetic head from the track center position, discloses a technique in which: a phase difference of a reproduced signal from a burst area is detected and based upon the detected phase difference, position deviation information is found.
In the reproduced signal processing of this type utilizing a conventional phase difference detection, however, although the precision of the position deviation information can be improved, phases of reproduced signals from at least two types of burst recording patterns need to be detected. For this reason, in this conventional system, magnetic sections need to be recorded by using at least two types of different patterns in the burst area, causing the problem that the formatting efficiency of the magnetic recording medium deteriorates.